- Preheat the oven to 350°F (175°C). Grease a 9x5-inch loaf pan and line with parchment paper. 
- In a bowl, whisk together flour, baking soda, and salt. Set aside. 
- In another bowl, whisk melted butter and brown sugar until smooth. Add eggs, mashed bananas, Greek yogurt, and vanilla extract, and mix until combined. 
- Gradually fold in the dry ingredients until just combined—don’t overmix! 
- In a small bowl, mix granulated sugar and cinnamon for the swirl. 
- Layer the batter: Pour half of the batter into the loaf pan, sprinkle half of the cinnamon-sugar mixture, then repeat with the remaining batter and cinnamon-sugar. Swirl with a knife. 
- Bake for 50-55 minutes, or until a toothpick inserted in the center comes out clean. 
- Let the bread cool in the pan for 10-15 minutes, then transfer to a wire rack. 
- Slice, serve, and enjoy!